New black hole simulator uses real star data

A new interactive program reveals the spectacular light show you'd see if you dared to wander close to a black hole. It demonstrates how the extreme gravity of a black hole could appear to shred background constellations of stars, spinning them around as though in a giant black washing machine.

The program's creators say it could be an excellent tool to familiarise people with the weird ways that black holes warp light. "It's useful for people to play around with the parameters to study how, for instance, a black hole would distort the constellation Orion," says Thomas Müller of the University of Stuttgart in Germany.

A black hole forms when a massive star explodes at the end of its life, the core collapsing to a point with huge density and an enormous gravitational pull. Even at a safe distance from the black hole, its gravity can distort the apparent positions of background stars, an effect called gravitational lensing.

Last year, scientists at the University of Colorado demonstrated a video of what you'd see if you fell into a black hole.

Now Müller and Stuttgart colleague Daniel Weiskopf have gone a step further, creating a program that lets you alter various inputs to tour a black hole's environs.

Real data

The program incorporates the real positions of around 118,000 stars mapped by the European Space Agency's Hipparcos satellite. Users can choose their distance from a black hole, then go into orbit or plunge straight in.

At the start of each tour, you see a black circle that marks the hole's event horizon – the boundary from which nothing, not even light, can escape. The light of background stars distorts as it passes close to the event horizon.

This example simulation shows the view while orbiting a black hole at a radius five times larger than the event horizon. In the background, the constellation Orion moves towards the black hole from the right, then gets shredded and spun around.

'Like a mirror'

"The constellation approaches the black hole, then you see stars like Betelgeuse – the left shoulder of Orion – appear twice, on the right and left sides of the black hole," Müller told New Scientist. "It's as if the black hole is like a mirror."

As well as accounting for gravitational lensing, the simulator shows how star colours would change near a black hole. The intense gravity makes background stars appear redder because it saps the energy of photons passing near the event horizon; the photons stretch to longer, redder wavelengths as they "climb out" of the gravitational trap.

But this effect is counteracted by your speed when you're falling freely towards a black hole – travelling at nearly the speed of light, stars in the black hole's backdrop turn bluer due to the Doppler effect. In a simulation mimicking such unhindered freefall, the light of the entire universe appears concentrated into a bright ring once you reach the middle of the black hole.

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